which can be explored by
neutrinoless double beta decay (\(0\nu \beta \beta \) ) experiments. Among the current experiments in operation, the KamLAND-Zen Collaboration[1]} has set the most stringent limit of \(m_{ee}< (0.061-0.165)\)  eV depending on the nuclear matrix element value of the \(^{136}\) Xe decays, while next-generation experiments aim for an improved sensitivity of \( m_{ee}\)  being up to 0.01 eV.
